1. Field of the Invention
The present invention relates to charge coupled device (CCD) imagers, and more particularly, to a method and means for extending the dynamic range of such imagers, to enable signal detection at illumination input conditions significantly greater than those at which CCD signal saturation is reached with conventional operating conditions, whereby signal information above the saturation level that would otherwise be lost is made available.
2. Prior Art
The need for extending the dynamic range of CCD imagers while avoiding the loss of low light signal response has resulted in the development of various methods that create a non-linear response in such devices, such as typified by that described in U.S. Pat. No. RE. 34,802 issued Nov. 29, 1994 to Michel Sayag. Essentially, the dynamic range of the pixels on a CCD sensing surface, which surface contains a plurality of pixels consisting of gate controlled charge integration wells, is limited by the charge handling capacity of the signal charge integration well sites. In the case when high intensity illumination is incident upon the CCD surface, the wells can saturate before the end of charge integration thus causing a large loss in signal response for high intensity scene information. Thus, such CCD sensing surfaces may not function satisfactorily when sensing scenes with very large in-scene variations in illumination level.
3. Problem to be Solved
Accordingly, a problem is presented by charge saturation and loss in signal response in such CCD environments, that limits the dynamic range of these imaging devices.
4. Objects
It is therefore an object of the present invention to provide a method and means for overcoming the integration well site charge saturation problem in CCD imagers.
It is another object of the invention to provide a structure and and an operating method that extends the dynamic range of CCD imagers to overcome the charge saturation problem in such imagers.